The class action lawsuit, filed in May, states that Google “unlawfully opens up, reads, and acquires the content of people’s private email messages” in violation of California’s privacy laws and federal wiretapping statutes.

The lawsuit also notes that the company scans messages sent to Gmail users from non-Gmail users, who never agreed to the company’s terms.

However, Google argues that all users of email must necessarily expect that their emails will be subject to automated processing.

"Just as a sender of a letter to a business colleague cannot be surprised that the recipient's assistant opens the letter, people who use Web-based email today cannot be surprised if their communications are processed,” Google said in a 39-page document filed in San Jose last year, calling for the dismissal of the class-action lawsuit.

“Indeed, a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties,” it added, citing a Supreme Court judgment handed down over electronic communications in 1979 – long before Google existed.